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In this study, in situ electrical biasing was combined with transmission electron microscopy (TEM) in order to study the formation and evolution of Wadsley defects and Magnéli phases during electrical biasing and resistive switching in titanium dioxide (TiO2). Resistive switching devices were fabricated from single-crystal rutile TiO2 substrates through focused ion beam milling and lift-out techniques. Defect evolution and phase transformations in rutile TiO2 were monitored by diffraction contrast imaging inside the TEM during electrical biasing. Reversible bipolar resistive switching behavior was observed in these single-crystal TiO2 devices. Biased induced reduction reactions created increased oxygen vacancy concentrations to such an extent that shear faults (Wadsley defects) and oxygen-deficient phases (Magnéli phases) formed over large volumes within the TiO2 TEM specimen. Nevertheless, the observed reversible formation/dissociation of Wadsley defects does not appear to correlate to resistive switching phenomena at these length scales. These defect zones were found to reversibly reconfigure in a manner consistent with charged oxygen vacancy migration responding to the applied bias polarity.

Electron diffraction in both SEM and TEM provides a contrast mechanism for imaging defects as well as a means for quantifying elastic strain. Electron backscatter diffraction (EBSD) is the commercially established method for SEM-based diffraction analysis. In EBSD, Kikuchi patterns are acquired by a charge-coupled device (CCD) camera and indexed using commercial software. Phase and crystallographic orientation information can be extracted from these Kikuchi patterns, and researchers have developed cross-correlation methods to measure strain as well.